Patent Literature 1 discloses a power-source noise detector circuit which applies noises to a circuit formed on a board, and which inspects whether or not such noises are conducted through a path over that circuit.
The power-source noise detector circuit disclosed in Patent Literature 1 includes a flip-flop, and when no noise is conducted through a power-source path, maintains the polarity of the output by the flip-flop. Conversely, when noises are conducted through the power-source path, the polarity of the output by the flip-flop is inverted. Next, when the polarity of the output by the flip-flop is inverted, the power-source noise detector circuit causes a light emitting diode to emit light. Through this light emission, the power-source noise detector circuit informs that noises are conducted through the power-source path.